Plated wire memory

ABSTRACT

A plated wire core memory array is described in which the core wires are divided into two sets which are placed on either side of word conductors. The flux emanating from one core during excitation passes through another core on the other side of the word conductors so that fluctuations in the switching fields due to changes in the pattern of stored information, are reduced or suppressed.

United States Patent 3,654,627 Snyder [4 Apr. 4, 1972 541 PLATED WIREMEMORY 3,397,394 8/1968 Maeda ..340/l74 PW [72] Inventor: l:Rlichard L.Snyder, New Smyrna Beach, Primary Examiner stanley MurynowiczJn 22Filed: June 30,1970 ABSTRACT 21 Appl. No.: 51,175

US. Cl. ..340/174 PW, 340/174 QB, 340/174 DC Int. Cl ..G1lc 11/14 Fieldof Search ..340/l74 PW, 174 PC, 174 QB, 340/174 DC References CitedUNITED STATES PATENTS 2/1968 Fedde ..340/l74 PW 0.. WRITE -3s AMPLIFIERWORD A plated wire core memory array is described in which the corewires are divided into two sets which are placed on either side of wordconductors. The flux emanating from one core during excitation passesthrough another core on the other side of the word conductors so thatfluctuations in the switching fields due to changes in the pattern ofstored information, are reduced or suppressed.

1 Claims, 3 Drawing Figures SENSE AMPLIFIER SELECTOR PLATED WIRE MEMORYThis invention is concerned with static magnetic core memories of thetype in which the core is a section of magnetic material deposited as athin film on a wire, such as that described in U.S. Pat. No. 3,390,383,issued to the applicant on June 25, 1968. The magnetic material isusually a nickel iron alloy deposited in an electroplating bath and sotreated that it is oriented having uniaxial anisotropy with the easyaxis in the circumferential direction.

Bits of information are stored in the memory by magnetizing sections ofthe film along a circumferential path in either a clockwise orcounterclockwise direction depending on the value of the bit. Storage iseffected by passing a current through the wire having its polaritydetermined by the value of the bit. This current generates acircumferential magnetic field which, acting alone, is somewhat lessthan that required to reverse the polarity or to disturb the field in amagnetized section of the wire. While this current is flowing, amagnetic field parallel to the axis is generated by passing currentthrough a short coil, called the word coil, around the wire. Itsconductors have straight sections positioned near each side of andsubstantially perpendicular to the wire. The width of the coil isapproximately equal to the length of the section of the film and wire inwhich a bit is stored. The combination of the circumferential and axialfields in the selected bit section causes the field in the magnetic filmto reverse by coherent or rotational switching if the film is notinitially magnetized in the direction of the field established by thebit wire current.

Information is read from a bit position by pulsing a current through theword coil equal to that used during recording. The magnetic field soproduced partially rotates the field stored in the bit section. Thispartial rotation of the field changes its coupling to the core wirethereby generating a voltage across the bit section which is detectedacross the terminals of the core wire. The polarity of the voltage soproduced is determined by the polarity of the stored bit. The field fromthe read pulse is limited to a value which, when the pulse subsides,allows the field in the film of the bit section to return to its initialcondition so that any number of read operations may be executed withoutdestroying the stored information.

The current through the core wire during recording is supplied through abridge circuit which is arranged so that the sensing circuit isprotected from excessive disturbance during recording. It is notintended that any discussion of ancillary equipment or circuitsconnected to the memory array to be described are to be considered asentering into this invention. Such equipment is well known to thoseskilled in the art. Only the array itself, including the core wires andword conductors and shields, are new.

In memories of this type, a number of bit wires are arranged in aparallel array and are served in parallel by a number of recording andsensing circuits. The array is also provided with a number of workcoils, each of which encloses all of the wires. A number of bits aretherefore served by each word coil and a number of words are served byeach bit wire. When a large number of bits are being switchedsimultaneously, a considerable magnetic field is developed near them.This field is variable depending on how many bits in a word areswitched. For this reason, it is usually necessary to space the bitwires relatively far apart to prevent bits adjacent to those beingswitched from being disturbed.

For example, consider an array composed of bit wires, 0.005 inches indiameter, a common size, having a magnetic film 10,000 angstroms thick.The circumference of the wire is therefore approximately 0.040centimeters. The total area of film is, in a cross section perpendicularto the axis, then 4 X 10 X 10 4 X 10 square centimeters. The saturatedflux density in these films is approximately 1.25 X 10' gauss.Therefore, a total of X lines would exist if the film were saturated inthe axial direction. This condition exists during rotational switchingof a core. If the array has its wires spaced on 0.010 inch centers orfour wires per millimeter and, due to shielding, the fields external tothe core sections are confined to a space I millimeter thick, the fluxdensity when all of the cores switch, will then be 4 X 5 X 10 0.2 linesper square millimeter or 20 gauss. A magnetic field of 20 oersteds inaddition to that required for overcoming the reluctance of the materialwould then be needed. However, if none of the cores switch, less thanhalf the 20 gauss must be accommodated. Since the difference between thefield required for switching and that for no switching is nearly aslarge as the usual cross fields from the word coils, such a system isinoperative. For this reason, the core wires are arrayed with muchgreater spacing.

Even with relatively large spacing between the bit wires variations inthe fields caused by changes in bit patterns place severe requirementson the tolerances that can be permitted in variations in thecharacteristics of the magnetic films. These requirements can beconsiderably relaxed if field variations are eliminated.

The present invention overcomes this problem of variable fields byemploying two cores per bit, placed close to one another and arranged sothat during switching the field emanating from one core is provided witha return path through its mating core. By this means, fluctuating fieldsabout the switching cores are eliminated which also eliminates patternsensitivity. Mention should be made of the fact that a compromise can bemade in which only one core per bit is used and pattern sensitivity canbe greatly reduced. In this scheme, cores are arranged in pairsindependently. The flux due to the word coil field is thereforecancelled. By arranging matters so that neighboring cores cannot switchtogether, interference is reduced.

It is accordingly an object of this invention to provide an improvedthin film memory.

Another object of this invention is to eliminate pattern sensitivity ina thin film memory.

A further object of the invention is to provide a means of making a morecompact plated wire memory array.

Still another object of the invention is to provide a memory structuremore compact than those presently available but to retain the economy ofa single core per bit.

One more object is to provide a structure for plated wire memories whichwill function with cores having less uniform magnetic characteristicsthan are now required.

The foregoing and other objects and features of this invention will bemore clearly understood from consideration of the detailed descriptionof embodiments thereof which follows when taken in conjunction with theaccompanying drawings in which:

FIG. 1. is a diagram which illustrates how the magnetic field in andabout the cores of a conventional plated wire memory behaves duringreading and writing.

FIG. 2 illustrates the behavior of cores in a memory made in accordancewith the present invention.

FIG. 3 is a semi-schematic diagram of a plated wire core memory havingtwo core sections to store each bit.

As mentioned above, the magnetic films of which the cores are made areso oriented that they have uniaxial anisotropy with the easy axisforming a circumferential path. In the absence of an externally appliedmagnetic field, this material can only be magnetized in the direction ofthe easy axis except where two magnetic domains meet. At the domainwalls for a distance of a few hundred molecules, the field undergoes areversal. FIG. 1 shows a bit wire 1 l on which for convenience areindicated four bit storage positions as discreet sections of film. Inpractice, the films are usually continuous with the ends of the bitpositions comprised of domain walls. At A in FIG. 1 is shown a sectionof film magnetized in one polarity indicated by the arrow 0. Its fieldwill be undisturbed even if it is subject to a reverse magnetizingcurrent IWI having the magnitude required to write a bit of the oppositepolarity. The Section at B is shown enclosed by the conductors of a wordcoil 12. It is initially magnetized in the same direction as section atA but is then subject to a magnetomotive force from current in the wordcoil generating the field H indicated at 4. H, causes the field in thefilm to tilt into a helical direction indicated by the arrow 2. Some ofthe flux emerges from the core and encircles the conductors of the coil12, as shown by the line 5, instead of the core wire 11. This change offlux linkage generates a voltage across the section at B. When the fieldfrom the coil 11 is allowed to collapse, the flux returns to its initialpath and in so doing, generates another voltage of opposite polarityacross the section at B. At C the same set of circumstances prevails asat B except that the polarity of the field in the core is reversed asindicated by the arrow 1. When the core at C is subject to the samemagnetizing force as at B, the flux tilts as shown by the arrow 3. Thepolarity of the emerging flux is the same as at B. However, the voltagesinduced across the section are opposite because the flux linking thewire has been reduced from the opposite polarity. The direction of thefield from the coil is immaterial, the polarity of the output signals issubject only to the polarity of the field in the film.

At D is shown a film initially magnetized in the direction. It is thensubject to a magnetizing force from the word coil 12 which tilts thefield in the direction of the arrow 2. The section is next subject tothe additional field from current lWl in the bit wire which causes theflux to swing to the position indicated by the arrow 3. When bothmagnetizing forces subside, the field in the core swings to the positionindicated by the arrow 1 being completely reversed.

As described above, the fields which emerge from the cores during areading or writing operation have magnitudes that are comparable tothose produced by the controlling currents. Because the magnitudes ofthese fields depend on whether a core switches or not, which is in turndetermined by the information being stored, no compensating changes inthe control currents can be employed to reduce the effects of thevariation.

Complete compensation can be obtained by using a structure like thatshown in FIG. 2. The word coil is replaced by a single conductor 23 andtwo shield plates 24 which provide space for two bit wires 21 and 22.All of the wires in the array are electrically insulated from oneanother and from the word conductors and the shields. The wordconductors are also insulated from the shields except that one end ofeach word conductor may be connected to the shields which then serve asa ground return. This insulation is not shown in the drawings. Currentthrough the word conductor 23 which may return through the shield plates24 generates a magnetic field parallel to the axis of 21 and 22 but inopposite directions so that a north pole formed by flux leaving the coreon 21 is adjacent to a south pole formed at the end of the core on 22.Since the cores are of reasonably uniform magnetic characteristics, verylittle field develops beyond them. When the cores switch, the increasedfield from each core compensates that from the other and no variation infield outside the region occurs. The direction of magnetization for thecores representing zero and ones relative to one another is immaterial.Thus, if 1 is used to record a zero in the core on 21, either 1 or I.may be used to record a zero in the core on 22. Of course, theconvention, once selected, must be maintained.

The independence of the core convention between pairs of cores make itconvenient to use either a series or a parallel system of excitation ofthe bit wires. FIG. 3 is a schematic diagram of a memory using two coresper bit. It consists of two arrays of word conductors 23 served by aword selector 39, four sets of bit wires 30,31,32, and 33 which areconnected to the primaries of four coupling transformers 34 which havingcenter taps 35 connected to four write circuits 38 only one of which isshown. The bit wires connected to each side of the primary of atransformer have substantially the same impedance. The secondaries 36 ofthe four transformers are connected to four sense amplifiers 37, onlyone of which is shown. Shields which are normally placed on either sideof each array are here omitted to simplify the diagram.

To record a word, the word selector 39 controlled by an externalcircuit, delivers a current pulse to one of the word conductors 23. Eachwrite amplifier delivers a pulse of current to the center tap 35 of oneof the transformers. The polarit of the pulse 18 determined by the valueof the bit to be recorded.

The current to each center tap divides between the two bit wires of eachpair in substantially equal amounts. The magnitude of the current isselected to cause no disturbance in any core except adjacent theselected word conductor.

To read a word, one of the word conductors is excited by the wordselector. The magnetizing force from the current in the word line tiltsthe field in all of the cores under its influence causing a voltage tobe generated across each bit section which excites the transformerprimary connected to its word line and causes a signal to be deliveredby the secondary to the sense amplifier. The polarity of the signalindicates the value of the bit stored in the disturbed cores.

It will be noticed in FIG. 3 that the branches of the bit wires 30 and31 are connected in parallel on either side of the transformer primarywhereas bit wires 32 and 33 are connected so that their branches areconnected in series. The parallel connection is suitable for largearrays where it is desirable to keep current paths short to minimizesignal propagation time. The series connection is used in small arrayswhere propagation time is negligible because less current is required.

The structures so far described achieve nearly complete suppression ofstray fields from switching cores. In very large memories, completesuppression may sometimes be unnecessary. in very large memories, thenumber of bit wires in an array may be many times the number of bits ina word. Consequently, only a small fraction of the bit wires will beexcited during the recording of a word.

If the bit wires to be selected for any word are uniformly distributedin the array, the spacing between the active bit wires may be greatenough to reduce interaction to negligible levels. By placing half thebit wires on one side of an array of word conductors and half on theother side, all stray fields due to word selection currents will besuppressed. Also switching of two of the most closely spaced cores whichwill be on opposite sides of the array will cancel each others strayfields.

A structure for a plated wire memory has been described in which it ispossible to store information at high density. Although the embodimentand its variations which have been described in detail above is one formof the invention, other configurations and embodiments may be made byone skilled in the art without departing from the spirit, scope, orprinciple of this invention.

What is claimed is:

1. A magnetic core memory array of the type in which the cores areformed in a ferromagnetic film deposited on a wire called a bit wiresaid cores consisting of magnetic flux in a path in the film whichencircles the wire and extends axially along the wire for a distancesubstantially equal to the core width; said memory array being comprisedof a group of said bit wires arranged in a parallel configurationwherein each wire passes an assembly of parallel word conductors saidbit wires to be arranged to be substantially perpendicular to andequally spaced from said word conductors; said group of bit wiresdivided into two sets one of which passes on one side of said wordconductors and one on the other side; said sets arranged so that thewires in one set are as close as it is practical to place them tocorresponding wires in the other set; said corresponding pairs of wiresfrom each set electrically connected in parallel so that the cores of apair on either side of a word conductor are subject to substantiallyequal electrical excitation, changing their magnetic fields in acomplementary manner and so suppress or reduce the effect of said fieldson neighboring cores.

1. A magnetic core memory array of the type in which the cores areformed in a ferromagnetic film deposited on a wire called ''''a bitwire'''' said cores consisting of magnetic flux in a path in the filmwhich encircles the wire and extends axially along the wire for adistance substantially equal to the core width; said memory array beingcomprised of a group of said bit wires arranged in a parallelconfiguration wherein each wire passes an assembly of parallel wordconductors said bit wires to be arranged to be substantiallyperpendicular to and equally spaced from said word conductors; saidgroup of bit wires divided into two sets one of which passes on one sideof said word conductors and one on the other side; said sets arranged sothat the wires in one set are as close as it is practical to place themto corresponding wires in the other set; said corresponding pairs ofwires from each set electrically connected in parallel so that the coresof a pair on either side of a word conductor are subject tosubstantially equal electrical excitation, changing their magneticfields in a complementary manner and so suppress or reduce the effect ofsaid fields on neighboring cores.